The present invention relates to an arc chamber for low-voltage circuit breakers, particularly for molded case power circuit breakers.
It is known that molded case power circuit breakers are normally used in industrial low-voltage electrical systems, i.e., systems operating at up to approximately 1000 Volt. Said circuit breakers are usually provided with a system which ensures the nominal current required for the various users, the connection and disconnection of the load, protection against any abnormal conditions, such as overloading and short-circuit, by automatically opening the circuit, and the disconnection of the protected circuit by opening the moving contacts with respect to the fixed contacts (galvanic separation) in order to achieve full isolation of the load with respect to the electric power source.
The critical function of interrupting the current (whether nominal, overload or short-circuit current) is provided by the circuit breaker in a specific portion of said circuit breaker which is constituted by the so-called deionizing arc chamber. As a consequence of the opening movement, the voltage between the contacts causes the dielectric discharge of the air, leading to the forming of the electric arc in the chamber. The arc is propelled by electromagnetic and fluid-dynamics effects inside a series of metal plates arranged in the chamber, which are meant to extinguish said arc by cooling.
During arc forming, the energy released by Joule effect is very high and causes thermal and mechanical stresses inside the plate containment region. In order to withstand these stresses, the design of the arc chamber must be evaluated carefully so as to obtain a component which is solid enough to withstand the mechanical stresses and clearly defined so as to appropriately guide the arc into the extinguishing region while providing protection of the regions that must not be affected. Also, it is a common practice to include in the arc chamber elements made of insulating materials capable of emitting gaseous substances in the presence of an electric arc. Such substances interact with the plasma ions generated by the arc, thereby contributing to the reduction of overall phenomenon by reducing the conductivity.
FIGS. 1 and 2 illustrate a typical example of an arc chamber of the prior art. The chamber generally comprises two side walls 1 made of insulating material, a plurality of metallic plates 2 and at least one protective element 3 made of insulating material. The plates 2 are generally U-shaped and have, at their outer lateral edges, a plurality of protrusions 21. The side walls 11 have a plurality of openings 11 which are suitable to mate with the corresponding protrusions 21 of the plates 2 (see FIG. 2) for plate positioning and fixing. Plate fixing is provided, for example, by upsetting the protrusions 21, thus ensuring containment of the plates and mechanical stability of the arc chamber. Once assembled, the arc chamber is inserted in an appropriately provided space formed in the case of the circuit breaker.
Although this solution adequately meets the necessary requirements, it is not entirely satisfactory in terms of the number of components required and of manufacturing complexity. In addition to the side walls made of insulating material, it is in fact also necessary to provide appropriate components (for example the protective element 3) for arc guiding/protection.
Furthermore, the fact must not be ignored that adequate mechanical stability is ensured only by virtue of the complicated operation of fixing the plates to the side walls, for example by upsetting the protrusions that are present on the edges of the plates.
The aim of the present invention is to provide an arc chamber for low-voltage circuit breakers, which is constituted by a limited number of components which is smaller than the number of components of conventional arc chambers.
Within the scope of this aim, an object of the present invention is to provide an arc chamber for low-voltage circuit breakers, which does not require complicated assembly steps.
Another object of the present invention is to provide an arc chamber for low-voltage circuit breakers, which has adequate mechanical stability without requiring complicated mechanical processes.
Another object of the present invention is to provide an arc chamber for low-voltage circuit breakers, which can be easily assembled inside the pole of the circuit breaker.
A further object of the present invention is to provide an arc chamber for low-voltage circuit breakers, which does not require the use of additional elements capable of emitting gaseous substances which reduce the arc-related phenomena. Another object of the present invention is to provide an arc chamber for low-voltage circuit breakers which is highly reliable, relatively easy to manufacture and at competitive costs.
This aim, these objects and others which will become apparent hereinafter are achieved by an arc chamber for low-voltage circuit breakers, characterized in that it comprises:
multiple substantially U-shaped metallic plates;
an enclosure made of insulating material which is substantially shaped like a parallelepiped and comprises two side walls, a bottom wall, a top wall and a rear wall, said side walls having, on the inside, multiple mutually opposite slots for the insertion of said metal plates, the bottom and top walls each having an opening, said enclosure being open at the front.
In this manner, one has the advantage of providing a mechanically stable arc chamber with a reduced number of components and of avoiding the complex mechanical operation of upsetting.